Many ion-generating devices that utilize a discharge phenomenon have been commercialized. These ion-generating devices are generally configured with an ion-generating element for generating ions, a high-voltage transformer for supplying a high voltage to the ion-generating element, a high voltage-generating circuit for driving the high-voltage transformer, and a power supply input unit such as a connector.
An example of the commercialized ion-generating elements includes the one that uses a metal wire, a metal plate having an acute-angled portion, a needle-like metal, or the like as a discharge electrode, and uses a metal plate, a grid, or the like at a ground potential as an induction electrode (counter electrode), or the one that uses the ground as an induction electrode and does not particularly dispose an induction electrode. In the ion-generating element of this type, the air serves as an insulator. This ion-generating element utilizes a scheme to produce a discharge phenomenon by causing electric field concentration at a tip of an electrode, which has as an acute-angled portion such as a needle-like portion to serve as a discharge electrode, when applying a high voltage to the electrode, and causing an electrical breakdown of the air in close vicinity of the tip.
An example of the ion-generating elements that utilize this scheme is a device disclosed in, for example, Japanese Patent Laying-Open No. 10-199653. This publication discloses a device which includes a discharge electrode provided with a needle-like metal, and a cylindrical electrode provided to face the discharge electrode, and serves for extracting negative ions generated as corona discharge occurs, to an outside of the device.
For another example, there is a device disclosed in Japanese Patent Laying-Open No. 2003-308947. The publication describes a configuration in which an induction electrode is disposed rearward (in a lateral surface position) with respect to a tip portion of a discharge electrode needle. The above publication discloses that the shape of the induction electrode may also be of a stick type, a plate type, a mesh type, or the like, and that the key point is not the shape of the induction electrode but the disposition thereof.